High speed microwave field effect transistors and Schottky diodes find application in high efficiency amplifiers (HEA's) and other microwave integrated circuit applications. Microwave field effect transistors include aluminum gallium nitride/gallium nitride heterojunction field effect transistors (AlGaN/GaN HFET's), gallium arsenide pseudomorphic high electron mobility transistors (GaAs pHEMT's), gallium arsenide metal-semiconductor field effect transistors (GaAs MESFET's), and silicon laterally diffused metal-oxide semiconductor (Si-LDMOS) transistors. High efficiency amplifiers operate in class B, class C, class D, class E, class F, inverse class F, and class S modes of operation. Theoretical efficiencies for these modes of operation may approach 100%. These classes of microwave power amplifier operation generally amplify waveforms wherein non-zero voltage and current do not simultaneously appear on the drains of amplifier final stage transistors. Non-overlapping voltages and currents require the transistors to operate in “switch-mode.” This means that the current that passes through such a transistor has a square wave shape. Therefore, the transistor must be able to have high current gain not only at the fundamental frequency, but at harmonic frequencies of the fundamental frequency so that square waves can be generated by the transistor. Maintaining high current gain at the fundamental and harmonic frequencies requires that the transistor have has a high unity gain cutoff frequency (fT). For example an HEA operating in a switch-mode of operation at a fundamental frequency of 4 gigahertz (GHz) may require greater than unity current gain at frequencies that exceed 40 GHz. Therefore a transistor with a fT of greater than 40 GHz is required for such an application.
Schottky diodes find applications in microwave circuits for detection, circuit protection, level shifting, switching, and other applications. In HEA's, Schottky diodes are particularly useful for protecting from over-voltage conditions due to inductive ringing or other transient effects when connected to the drains of field effect transistors. Depending on the application, power, and frequency level, designers may use submicron gate AlGaN/GaN HFET's, GaAs pHEMT's, GaAs MESFET's, or Si-LDMOS devices in conjunction with Schottky diode devices to realize HEA's. The transistor devices may be fabricated using electron-beam lithography techniques. Accordingly, designers desire structures and methods that increase the functionality and manufacturing ease of such devices.